The present invention relates to chemical mechanical polishing (CMP) tools, and more particularly, to cleaning apparatuses for use in CMP tools.
Chemical mechanical polishing (CMP) tools are typically used to planarize the surface of a semiconductor wafer or to remove a portion of a layer formed on the semiconductor wafer, undergoing fabrication of circuits thereon, by processes such as the damascene and dual damascene. Some CMP tools also include a mobile or stationary carrier to hold a wafer, and a mobile or stationary platen or table equipped with a polish pad. The CMP tool imparts relative motion between the wafer surface and the polish pad. The CMP tool causes the polish pad and the wafer surface to come into contact, typically applying a specified pressure between the polish pad and the wafer surface sufficient to thereby polish the wafer surface, by removal of some material from its surface. In addition, the CMP tool typically introduces a slurry or reactive chemical at the interface between the polish pad and the wafer surface. The slurry can have abrasive particles suspended in a chemical solution that reacts with selected materials on the wafer surface. The pressure, slurry and relative motion effectuate the polishing process.
Typically at the end of a CMP process step there is a subsequent cleaning step to remove debris and residual slurry. Some cleaning apparatuses place the wafer in a horizontal position with a cleaning solution being applied to permit effective cleaning with the brush. Because each wafer is being cleaned in a horizontal position, the cleaning apparatus may occupy a relatively large footprint, especially if multiple wafers are being cleaned. Further, the trend in the industry is to increase wafer size, which will tend to further increase cleaning apparatus footprints. Moreover, horizontal apparatuses undesirably have a relatively large contact area between the wafer and the fabrication environment, which might increase the risk of contamination of the wafer and/or the clean room environment. Additionally, due to industry demand for increased throughput, there is a need for the ability to clean multiple wafers simultaneously. Therefore, there is a need for an alternative to prior art apparatuses and methods of cleaning wafers.
In accordance with embodiments of the present invention, a multiple wafer (or workpiece) cleaning apparatus is provided that permits cleaning of multiple wafers simultaneously while maintaining a relatively small footprint in the fabrication environment.
In one embodiment of the present invention, the cleaning apparatus includes a first pair of spaced-apart brushes with supports for holding a workpiece, and a second pair of spaced-apart brushes, with supports for holding another workpiece. The brushes are rotatable, with one of each pair of brushes movable axially toward the other brush of the pair so that the brushes contact a workpiece with a controlled pressure.
In another embodiment the invention utilizes a controller in communication with pairs of brushes. The controller causes the brushes to rotate and come into contact with the workpieces. Parameters such as the axial brush forces, cleaning cycle duration, brush rotation speeds, and rotation directions of the pairs of brushes are controllable via signals provided by the controller in this embodiment.
In a further embodiment of the present invention, the diameter of each brush assembly may be greater than the radius of the wafers. During the cleaning process, the workpieces are loaded into the machine and supported, with the center of the workpiece being offset from the center of rotation of the brushes. During cleaning, the brushes are brought into contact with opposite sides of the wafers and the brushes are rotated, thereby causing the workpiece to rotate through frictional forces. This embodiment of the invention advantageously eliminates the need for a separate unit to rotate the workpieces, although such a unit may be used in conjunction with the brushes, as described here.
According to another embodiment of the present invention, the brushes can each rotate at the same speed, different speeds or in different directions, thereby creating a differential relative velocity between the brushes and the workpiece surfaces resulting in forces tangential to the workpiece surfaces that assist in cleaning the workpieces. Cleaning fluid can be introduced to the workpiece surface or issued directly through the brush material or through distribution holes in the brushes.
In another embodiment of the present invention, a cleaning fluid is introduced to at least a portion of the workpieces to facilitate the cleaning process. The fluid can be used to flush away and/or react with debris, which has accumulated on the workpieces. In yet another embodiment of the present invention, the apparatus includes a tank or tanks to hold the fluid, with at least a portion of the workpieces being submerged so that the workpieces rotate through the fluid. This allows the workpieces to more readily contact the cleaning solution to assist the brushes in the cleaning the workpieces. In still another embodiment the tanks can be filled to completely submerge the wafers.
In a further embodiment of the invention, a megasonic transducer is introduced into the cleaning solution tanks so that sonic waves further assist in cleaning portions of the workpieces submerged in the cleaning solution, as the workpieces rotate.
Additionally, in yet another embodiment of the invention there are no brushes, but instead the workpiece rests on support rollers at least one of which is coupled to a drive motor. This embodiment allows for brushless cleaning primarily using the cleaning solution, optionally in conjunction with the megasonic transducers.